Transport device, recording device, and medium transport method

ABSTRACT

A control device of a transport device includes a control unit configured to control a roll motor for rotating a first rotary shaft on which a medium is held and a transport motor for rotating a first driving roller, a tension detection unit configured to derive, for each tension detection cycle, a detected tension value of a tension applied to a tension adjustment portion of the medium, and a tension F/B unit configured to calculate a tension F/B correction amount by feedback control based on a deviation between a target tension and the detected tension value. The control unit is configured to calculate a driving force by the roll motor based on the tension F/B correction amount, and control the roll motor based on the driving force.

The present application is based on, and claims priority from JPApplication Serial Number 2018-162583, filed Aug. 31, 2018, thedisclosure of which is hereby incorporated by reference herein in itsentirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a transport device for unwinding amedium from a roll body and transporting the medium, a recording devicefor performing recording onto the medium transported by the transportdevice, and a medium transport method in the transport device.

2. Related Art

JP-A-2015-231910 describes an example of a recording device forunwinding a medium from a roll body and performing recording onto themedium. The recording device includes a holding unit configured torotatably hold the roll body, and a transport unit configured to unwindthe medium from the roll body for each predetermined transport cycle.The transport unit operates to feed the medium unwound from the rollbody, downstream in the transport direction.

Furthermore, the recording device described in JP-A-2015-231910 isconfigured to suppress fluctuation of a tension applied to the mediumbetween the roll body and the transport unit. Specifically, the tensionapplied to the medium between the roll body and the transport unit isdetected multiple times per transport cycle. Thus, in the recordingdevice, an average value of the tension applied to the medium betweenthe roll body and the transport unit in a previous transport cycle iscalculated, and the detected tension value in the previous transportcycle is calculated based on the average value. Further, in thefollowing transport cycle, a target tension, being a target value of thetension, is calculated based on the detected tension value for theprevious transport cycle, and the operation of the transport unit iscontrolled based on the target tension.

When a significant amount of the medium is transported in a singletransport cycle, the tension applied to the medium between the roll bodyand the transport unit may significantly fluctuate during the singletransport cycle. When the tension significantly fluctuates during asingle transport cycle, as described above, sufficient tension controlin a single transport cycle cannot be provided in the recording devicein which a target tension for the current transport cycle is calculatedbased on a detected tension value for the previous transport cycle andthe transport unit is controlled based on the target tension.

SUMMARY

A transport device for solving the at least one of above-describedproblems includes a holding unit configured to rotatably hold a rollbody formed by winding a medium, a rotary driving unit configured toimpart, to the holding unit, a driving force in a rotation direction ofthe roll body, a transport unit disposed downstream from the holdingunit in a transport direction of the medium, the transport unit beingconfigured to feed, downstream in the transport direction and for eachpredetermined transport cycle, the medium unwound from the roll body, atransport driving unit configured to drive the transport unit, a controlunit configured to control the rotary driving unit and the transportdriving unit, a tension detection unit configured to derive, for eachtension detection cycle that is shorter than the transport cycle, adetected tension value that is a tension applied to a portion of themedium between the holding unit and the transport unit, and a tensionfeedback unit configured to calculate, each time the detected tensionvalue is detected, a tension feedback correction amount by feedbackcontrol based on a deviation between the detected tension value and atarget tension that is a target value of the detected tension value. Inthe transport device, the control unit is configured to calculate, foreach tension detection cycle, a driving force by the rotary driving unitbased on the tension feedback correction amount to control the rotarydriving unit based on the driving force by the rotary driving unit.

A recording device for solving the at least one of above-describedproblems includes the above-described transport device and a recordingunit configured to perform recording onto a portion of the mediumtransported by the transport device, the portion being locateddownstream from the transport unit in the transport direction.

A medium transport method for solving the at least one ofabove-described problems includes prividing, a transport deviceincluding a holding unit configured to rotatably hold a roll body formedby winding a medium, a rotary driving unit configured to impart, to theholding unit, a driving force in a rotation direction of the roll body,a transport unit disposed downstream from the holding unit in atransport direction of the medium, the transport unit being configuredto feed the medium, unwound from the roll body, downstream in thetransport direction for each predetermined transport cycle, and atransport driving unit configured to drive the transport unit, deriving,for each tension detection cycle that is shorter than the transportcycle, a detected tension value that is a tension applied to a portionof the medium between the roll body and the transport unit, calculating,each time the detected tension value is derived, a tension feedbackcorrection amount by feedback control based on a deviation between thedetected tension value and a target tension that is a target value ofthe detected tension value, and calculating, for each tension detectioncycle, a driving force by the rotary driving unit based on the tensionfeedback correction amount to drive the rotary driving unit based on thedriving force by the rotary driving unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a recording deviceaccording to an embodiment.

FIG. 2 is a block diagram illustrating a functional configuration of acontrol device of the recording device.

FIG. 3 is a graph of an eccentricity profile.

FIG. 4 is a graph of a target tension profile.

FIG. 5 is a graph of a target transport speed profile.

FIG. 6 is a flow chart illustrating an eccentricity measurement process.

FIG. 7 is a flow chart illustrating a processing routine performed incalculation of a tension feedforward correction amount.

FIG. 8 is a flow chart illustrating a processing routine performed incalculation of a tension feedback correction amount.

FIG. 9 is a flow chart illustrating a medium transport method accordingto the embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

An embodiment of a transport device, a recording device, and a mediumtransport method will be described below in accordance with FIGS. 1 to9.

As illustrated in FIG. 1, a recording device 10 according to theembodiment is an ink-jet printer configured to record an image on amedium 100 by depositing ink being an example of a liquid onto themedium 100 such as paper. The recording device 10 includes a transportdevice 20 configured to transport the medium 100 in the transportdirection X, and a record unit 40 configured to record an image on themedium 100 transported by the transport device 20. The record unit 40 isan example of a “recording unit”.

A support 11 is configured to support a portion of the medium 100transported by the transport device 20, and the record unit 40 isconfigured to record an image on a recording surface 101 of thesupported portion of the medium 100. The record unit 40 includes a guidemember 41 extending along a scanning axis Y, and a carriage 42 supportedby the guide member 41. The scanning axis Y runs along a directionintersecting the transport direction X and along the recording surface101 of the medium 100 supported by the support 11. The carriage 42 issupported on the guide member 41 such that the carriage 42 can movealong the scanning axis Y. The carriage 42 includes a recording head 43configured to discharge ink droplets. The record unit 40 records animage on the recording surface 101 of the medium 100 by discharging inkdroplets from the recording head 43 toward the medium 100 while thecarriage 42 moves along the scanning axis Y.

As illustrated in FIG. 1, the medium 100 to be transported by thetransport device 20 is roll paper being an example of an elongatemedium. The transport device 20 includes a first rotary shaft 21configured to rotatably hold a roll body R1 formed by an unrecordedmedium 100 being wound into a cylindrical shape, and a roll motor 22being a power source for rotating the first rotary shaft 21. When theroll motor 22 applies a driving force to the first rotary shaft 21 torotate the roll body R1 in a feeding direction C1, the medium 100 is fedfrom the roll body R1. Thus, in the embodiment, the first rotary shaft21 corresponds to an example of the “holding unit”, and the roll motor22 corresponds to an example of the “rotary driving unit”.

A first driving roller 23 and a first driven roller 24 configured tosandwich the medium 100 against the first driving roller 23 are disposedbetween the first rotary shaft 21 and the support 11 in the transportdirection X of the medium 100. The first driving roller 23 rotates asthe driving force by a transport motor 25 is input. Thus, in theembodiment, the first driving roller 23 and the first driven roller 24correspond to an example of the “transport unit” disposed downstreamfrom the first rotary shaft 21 in the transport direction X of themedium 100. Further, the transport motor 25 corresponds to an example ofthe “transport driving unit” being the power source for the firstdriving roller 23.

The transport motor 25 is provided with a speed sensor 61 configured todetect a rotational speed Vtm of the output shaft of the transport motor25. An output signal of the speed sensor 61 is output to a controldevice 50 in the recording device 10.

A second driving roller 26 and a second driven roller 27 configured tosandwich the medium 100 against the second driving roller 26 aredisposed downstream from the support 11 in the transport direction X ofthe medium 100. The second driving roller 26 rotates as the drivingforce by the transport motor 25 is input. Note that, there may beanother motor, which is not the transport motor 25, serving as a powersource for the second driving roller 26, as long as the other motor canrotate the second driving roller 26 in synchronization with the firstdriving roller 23.

A second rotary shaft 28 is provided downstream from the second drivingroller 26 and the second driven roller 27 in the transport direction Xof the medium 100. The second rotary shaft 28 is configured to berotated in a winding direction C2 by the driving force of a windingmotor 29. As the second rotary shaft 28 rotates in the winding directionC2, the medium 100 fed by the second driving roller 26 and the seconddriven roller 27 is wound around the second rotary shaft 28. In otherwords, the second rotary shaft 28 is configured to hold a roll body R2being a roll of the recorded medium 100.

As illustrated in FIG. 1, the control device 50 of the recording device10 includes a CPU 51, a memory 52, and an ASIC 53. ASIC 53 is anabbreviation for “Application Specific IC”. The memory 52 is configuredto store programs to be executed by the CPU 51, various maps,calculation results by the CPU 51, values detected by various sensors,and the like. Further, the control device 50 is configured to controlthe transport device 20 and the record unit 40 to record an image on therecording surface 101 of the medium 100. Note that, the control device50 may include a plurality of CPUs, and a plurality of functions of theCPU 51 may be distributed to each of the plurality of CPUs. The memory52 and the ASIC 53 are also the same.

FIG. 2 illustrates a functional configuration for controlling the rollmotor 22 and the transport motor 25 in the control device 50. A firstdriving force base value deriving unit M11 is configured to derive abase value DRb1 of the driving force by the roll motor 22. For example,the first driving force base value deriving unit M11 is configured toderive, as the base value DRb1, a value that is preset depending on thesize of the roll body R1.

As illustrated in FIG. 1, a portion of the medium 100 unwound from theroll body R1 and located between the first rotary shaft 21 and the firstdriving roller 23 is referred to as a tension adjustment portion 100 a.In the embodiment, when the medium 100 is transported in the transportdirection X, the tension to be applied to the tension adjustment portion100 a of the medium 100 is adjusted. Thus, the first driving force basevalue deriving unit M11 may calculate the base value DRb1 that can givea target value of the tension to be applied to the tension adjustmentportion 100 a.

A tension detection unit M14 is configured to derive, in a predeterminedtension detection cycle Ttdc, a detected tension value TENd being adetection value of a tension applied to the tension adjustment portion100 a of the medium 100. As the tension applied to the tensionadjustment portion 100 a increases, the load to be applied to thetransport motor 25 being the power source for the first driving roller23 also tends to increase. Furthermore, as the load increases, the loadcurrent flowing through the transport motor 25 tends to increase. Thus,the tension detection unit M14 is configured to monitor the load currentflowing through the transport motor 25 to derive the detected tensionvalue TENd. In other words, the load current flowing through thetransport motor 25 is substantially proportional to the degree of thetension applied to the tension adjustment portion 100 a. Note that, whena sensor that can directly detect the load applied to the tensionadjustment portion 100 a is provided in the transport device 20, thetension detection unit M14 may calculate the detected tension value TENdbased on an output signal of the sensor.

A target tension profile storage unit M15 is an example of a “storageunit”, and configured to store a target tension profile PRTen being atransition of a target tension TENTr being a target value of thetension, over time in a predetermined transport cycle Ttc. The transportcycle Ttc refers to a period from a time point at which a transportationof the medium 100 is started to a time point at which the transportationof the medium 100 is stopped. In other words, the first driving roller23 and the driven roller 24 as the transport unit perform intermittenttransport by the transport cycle Ttc. In the intermittent transport, arecording operation by the record unit 40 and a transporting operationby the transport unit are performed alternatively. Further, thetransport cycle Ttc is sufficiently longer than the tension detectioncycle Ttdc. Therefore, during a single transport cycle Ttc, the tensiondetection unit M14 derives the detected tension value TENd a pluralityof times.

FIG. 4 shows an example of the target tension profile PRTen. The targettension profile PRTen represents a transition of the target tensionTENTr over time in a single transport cycle Ttc. As shown in FIG. 4, inan initial stage of a single transport cycle Ttc, the target tensionTENTr increases. Then, once the target tension TENTr reaches apredetermined value TEN1, the target tension TENTr is kept at thepredetermined value TEN1. In addition, in a final stage of the transportcycle Ttc, the target tension TENTr decreases.

Returning to FIG. 2, a tension feedback unit M16 includes a targettension setting unit M17 and a first calculation unit M18. Hereinafter,the tension feedback unit M16 is abbreviated as “tension F/B unit M16”.

The target tension setting unit M17 uses the target tension profilePRTen stored in the target tension profile storage unit M15 to set atarget tension TENTr. In other words, when the tension detection unitM14 detects the detected tension value TENd for the n-th tensiondetection cycle Ttdc in the transport cycle Ttc, the target tensionsetting unit M17 reads out, from the target tension profile PRTen, thetarget tension TENTr corresponding to the n-th tension detection cycleTtdc. For example, since the product of “n” and the tension detectioncycle Ttdc corresponds to a time in the transport cycle Ttc, the targettension setting unit M17 reads out, from the target tension profilePRTen, the target tension TENTr corresponding to the time. Note that, ineach tension detection cycle Ttdc in a single transport cycle Ttc, “n”is incremented by “1”. Further, when the transport cycle Ttc ends, the“n” is reset to “0”.

For each tension detection cycle Ttdc, the first calculation unit M18calculates a tension feedback correction amount ΔDRfb by the feedbackcontrol based on the deviation between the target tension TENTr set bythe target tension setting unit M17 and the detected tension value TENdderived by the tension detection unit M14. Hereinafter, the tensionfeedback correction amount ΔDRfb is abbreviated as “tension F/Bcorrection amount ΔDRfb”. Specifically, the first calculation unit M18calculates the tension F/B correction amount ΔDRfb by feedback controlbased on a deviation between the target tension TENTr corresponding tothe n-th tension detection cycle Ttdc in the transport cycle Ttc and thedetected tension value TENd for the n-th tension detection cycle Ttdc.

In the embodiment, the first calculation unit M18 calculates, as atension F/B correction amount ΔDRfb, a sum of a proportional element, anintegral element, and a differential element, when the deviation betweenthe target tension TENTr and the detected tension value TENd is used asinput. The first calculation unit M18 may calculate the tension F/Bcorrection amount ΔDRfb by using only some elements of the proportionalelement, the integral element, and the differential element.

As described in detail below, the first calculation unit M18 isconfigured to appropriately change a gain of the feedback control forcalculating the tension F/B correction amount ΔDRfb. A method ofchanging the gain will be described later.

Returning to FIG. 2, an eccentricity profile generating unit M12 isconfigured to generate an eccentricity profile PREcc of the roll bodyR1. In other words, the eccentricity profile generating unit M12performs an eccentricity measurement process for measuring theeccentricity of the roll body R1 held on the first rotary shaft 21.Then, the eccentricity profile generating unit M12 generates theeccentricity profile PREcc based on an eccentricity state of the rollbody R1 measured in the eccentricity measurement process.

Here, a case in which the first driving roller 23 and the first drivenroller 24 are not eccentric and no slippage occurs between the firstdriving roller 23 and the medium 100 and between the first driven roller24 and the medium 100 during transportation of the medium 100 isdescribed. In this case, the transport length of the medium 100transported in the transport direction X by the first driving roller 23and the first driven roller 24 per transport cycle Ttc is equal to thelength of the medium 100 unwound from the roll body R1 per transportcycle Ttc. Further, when the roll body R1 is not eccentric, the lengthof the medium 100 unwound from the roll body R1 per transport cycle Ttcis constant. However, when the roll body R1 is eccentric, the length ofthe medium 100 unwound from the roll body R1 per transport cycle Ttc isconstant, but the radius of the roll body R1 may vary in each transportcycle Ttc as the roll body R1 rotates. As a result, the tensionadjustment portion 100 a of the medium 100 may be excessively loosenedor strained, resulting in a fluctuation of the degree of tension in thetension adjustment portion 100 a. In addition, when the radius of theroll body R1 fluctuates cyclically as the roll body R1 rotates, therotational load applied to the roll motor 22 also fluctuates, and thus,the degree of tension may fluctuate.

Thus, in the embodiment, the eccentricity profile PREcc is generated torepresent the relationship between a rotation angle θr of the roll bodyR1 and the load current flowing through the transport motor 25 when theroll body R1 is rotated at a constant speed. In other words, when theroll body R1 is eccentric, the load current flowing through thetransport motor 25 fluctuates depending on the change in the rotationangle θr of the roll body R1. Since the load current flowing through thetransport motor 25 is proportional to the degree of tension, therelationship between the rotation angle θr of the roll body R1 and thefluctuation in tension can be known based on the eccentricity profilePREcc. FIG. 3 shows an example of an eccentricity profile PREcc.Essentially, the vertical axis in FIG. 3 should be represented as theload current flowing through the transport motor 25. However, asdescribed above, the load current flowing through the transport motor 25is substantially proportional to tension, so the vertical axis in FIG. 3represents tension. The eccentricity measurement process will bedescribed in detail later.

Returning to FIG. 2, a tension feedforward unit M13 utilizes theeccentricity profile PREcc generated by the eccentricity profilegenerating unit M12. Hereinafter, the tension feedforward unit M13 isabbreviated as “tension F/F unit M13”. Based on the eccentricity profilePREcc, when there is a likelihood of increase in tension, the tensionF/F unit M13, for example, sets a tension feedforward correction amountΔDRff to a smaller value as compared to when there is no likelihood ofincrease in tension. Hereinafter, the tension feedforward correctionamount ΔDRff is abbreviated as “tension F/F correction amount ΔDRff”.Note that details of the calculation process for the tension F/Fcorrection amount ΔDRff by the tension F/F unit M13 will be describedlater.

In the following description, the tension in the tension adjustmentportion 100 a is simply referred to as tension.

A control unit M20 is configured to calculate a driving force DR by theroll motor 22 based on the base value DRb1 derived by the first drivingforce base value deriving unit M11, the tension F/F correction amountΔDRff calculated by the tension F/F unit, and the tension F/B correctionamount ΔDRfb calculated by the tension F/B unit M16. In other words, thecontrol unit M20 calculates the driving force DR using the followingrelational equation (Equation 1). Further, the control unit M20 controlsthe roll motor 22 based on the calculated driving force DR.

DR=DRb 1+ΔDRff+ΔDRfb   (Equation 1)

In the relational equation (Equation 1), “DRb1+ΔDRff” is the drivingforce including the results of the feedforward control. When thatdriving force cannot eliminate the divergence between the detectedtension value TENd and the target tension TENTr, “ΔDRfb” is added. Thus,the calculation result of the above-described relational equation(Equation 1) is obtained as the driving force DR. In other words, avalue including both of the results of the feedforward control and thefeedback control is obtained as the driving force DR.

A second driving force base value deriving unit M31 is configured toderive a base value DTb1 of the driving force by the transport motor 25.For example, the second driving force base value deriving unit M31derives a preset value as the base value DTb1.

As illustrated in FIG. 1, a portion of the medium 100 between the firstdriving roller 23 and the second driving roller 26 is referred to as aspeed adjustment portion 100 b of the medium 100. In the embodiment,when the medium 100 is transported in the transport direction X, thetransport speed of the speed adjustment portion 100 b of the medium 100is adjusted. Thus, the second driving force base value deriving unit M31may calculate the base value DRb1 that can give a target value of thetransport speed in the speed adjustment portion 100 b. Hereinafter, thetransport speed in the speed adjustment portion 100 b is simply referredto as the transport speed.

Returning to FIG. 2, a transport speed deriving unit M32 is configuredto calculate the rotational speed Vtm of the output shaft of thetransport motor 25 based on an output signal of the speed sensor 61. Thetransport speed of the speed adjustment portion 100 b of the medium 100tends to increase as the rotational speed Vtm of the output shaft of thetransport motor 25 increases. Thus, the transport speed deriving unitM32 derives a detected transport speed value VTSd such that the detectedtransport speed value VTSd of the speed adjustment portion 100 bincreases, as the calculated rotational speed Vtm of the output shaft ofthe transport motor 25 increases.

In the embodiment, the transport speed deriving unit M32 is configuredto derive, in a predetermined speed detection cycle Tsdc, a detectedtransport speed value VTSd, and the speed detection cycle Tsdc isshorter than a single transport cycle Ttc. The speed detection cycleTsdc is shorter than the tension detection cycle Ttdc described above.

A speed profile storage unit M33 is configured to store a speed profilePRV being a transition of a target transport speed VTSTr over time in asingle transport cycle Ttc.

FIG. 5 shows an example of the speed profile PRV. As shown in FIG. 5,the speed profile PRV includes an acceleration segment RA, a constantspeed segment RC, which is a segment following the acceleration segmentRA, and a deceleration segment RD, which is a segment following theconstant speed segment RC. The acceleration segment RA is a segmentwhere the transport speed of the medium 100 increases over time. Theconstant speed segment RC is a segment where the transport speed of themedium 100 is constant over time. In the constant speed segment RC, thetransport speed may not be strictly constant as long as the transportspeed of the medium 100 is substantially constant over time. Thedeceleration segment RD is a segment where the transport speed of themedium 100 decreases over time.

Note that the acceleration segment RA may include a segmentcorresponding to a certain period of time after the target transportspeed VTSTr has been kept at a predetermined speed VTS1. In other words,the acceleration segment RA may be considered to include a segmentcorresponding to a certain period of time before the detected transportspeed value VTSd converges to the predetermined speed VTS1 by executionof the feedback control. In this case, the length of the period fromwhen the target transport speed VTSTr reaches the predetermined speedVTS1 to when the detected transport speed value VTSd converges to thepredetermined speed VTS1 is preset based on experimentation, simulation,or the like.

Returning to FIG. 2, a speed feedback unit M34 includes a targettransport speed setting unit M35 and a second calculation unit M36.Hereinafter, the speed feedback unit M34 is abbreviated as “speed F/Bunit M34”.

The target transport speed setting unit M35 uses the speed profile PRVstored in the speed profile storage unit M33 to set the target transportspeed VTSTr. In other words, when the transport speed deriving unit M32derives the detected transport speed value VTSd in the m-th speeddetection cycle Tsdc in the transport cycle Ttc, the target transportspeed setting unit M35 reads out, from the speed profile PRV, the targettransport speed VTSTr corresponding to the m-th speed detection cycleTsdc. For example, since the product of “m” and the speed detectioncycle Tsdc corresponds to a time in the transport cycle Ttc, the targettransport speed setting unit M35 reads out, from the speed profile PRV,the target transport speed VTSTr corresponding to the time. Note that,in each speed detection cycle Tsdc in a single transport cycle Ttc, “m”is incremented by “1”. Further, when the transport cycle Ttc ends, “m”is reset to “0”.

In each transport cycle Ttc, the second calculation unit M36 calculatesa speed feedback correction amount ΔDTfb by the feedback control basedon the deviation between the target transport speed VTSTr set by thetarget transport speed setting unit M35 and the detected transport speedvalue VTSd derived by the transport speed deriving unit M32.Hereinafter, the speed feedback correction amount ΔDTfb is abbreviatedas “speed F/B correction amount ΔDTfb”. Specifically, the secondcalculation unit M36 calculates the speed F/B correction amount ΔDTfb byfeedback control based on a deviation between the target transport speedVTSTr corresponding to the m-th speed detection cycle Tsdc in thetransport cycle Ttc and the detected transport speed value VTSd in them-th speed detection cycle Tsdc.

In the embodiment, the second calculation unit M36 calculates, as thespeed F/B correction amount ΔDTfb, a sum of a proportional element, anintegral element, and a differential element, when the deviation betweenthe target transport speed VTSTr and the detected transport speed valueVTSd is used as input. The second calculation unit M36 may calculate thespeed F/B correction amount ΔDTfb by using only some elements of theproportional element, the integral element, and the differentialelement.

The control unit M20 calculates a driving force DT by the transportmotor 25 based on the base value DTb1 derived by the second drivingforce base value deriving unit M31 and the speed F/B correction amountΔDTfb calculated by the speed F/B unit M34. In other words, the controlunit M20 uses the following relational equation (Equation 2) tocalculate the driving force DT. Further, the control unit M20 controlsthe transport motor 25 based on the calculated driving force DT.

DT=DTb 1+ΔDTfb   (Equation 2)

Next, the eccentricity measurement process to be performed by theeccentricity profile generating unit M12 of the control device 50 willbe described with reference to FIG. 6. The eccentricity measurementprocess is performed when a predetermined execution condition, includingwhen recording is not performed on the medium 100, is satisfied.

In a first step S11 of the eccentricity measurement process, thetransport device 20 is actuated to start transport of the medium 100. Ina following step S12, it is determined whether the driving force beingoutput from the roll motor 22 is constant. When the driving force beingoutput from the roll motor 22 is still fluctuating, it is not determinedthat the driving force being output from the roll motor 22 is constant.Further, when it is not determined that the driving force is constant(S12: NO), the determination of step S12 is repeated. On the other hand,when it is determined that the driving force is constant (S12: YES), theprocess proceeds to the next step S13.

In step S13, fluctuation in tension due to eccentricity is measured.Specifically, when an amount of the medium 100 unwound from the rollbody R1 per transport cycle Ttc by the first driving roller 23 and thefirst driven roller 24 is constant, the load current flowing through thetransport motor 25 is measured at each rotation angle θr of the rollbody R1. When the tension adjustment portion 100 a of the medium 100 isnot slackened, the amount of the medium 100 unwound from the roll bodyR1 by the first driving roller 23 and the first driven roller 24 isequal to the amount of the medium 100 to be transported per transportcycle Ttc. Accordingly, step S13 is preferably performed when thetension adjustment portion 100 a of the medium 100 is not slackened. Asa result, fluctuation in the rotational load applied to the roll motor22 due to the eccentricity is more correctly reflected in the loadcurrent flowing through the transport motor 25, resulting in improvingthe measuring accuracy. Such measurements are performed at a pluralityof rotation angles θr to measure a transition in the load currentflowing through the transport motor 25. Then, once the load at each ofthe rotation angles θr is acquired, the process proceeds to the nextstep S14. In step S14, the eccentricity profile PREcc is generated.Specifically, the tension tends to increase, as the load current flowingthrough the transport motor 25 increases. Thus, the eccentricity profilegenerating unit M12 measures the relationship between the rotation angleθr of the roll body R1 and the load current flowing through thetransport motor 25 at a plurality of points to generate an eccentricityprofile PREcc. Further, once the eccentricity profile PREcc isgenerated, the eccentricity measurement process ends.

Note that a current sensor (not illustrated) can be used as a means formeasuring the load current. Note that, a known means such as anelectrical resistance type device and a magnetic type device can be usedas the current sensor, for example.

Next, a processing routine to be performed by the tension F/F unit M13of the control device 50 to calculate the tension F/F correction amountΔDRff will be described with reference to FIG. 7. This processingroutine is repeatedly performed in each tension detection cycle Ttdcwhen the medium 100 is transported by the transport device 20.

In a first step S21 of the processing routine, it is determined whetherthe eccentricity profile generating unit M12 has generated theeccentricity profile PREcc. When it is not determined that theeccentricity profile PREcc has been generated (S21: NO), the processproceeds to the next step S22. In step S22, the tension F/F correctionamount ΔDRff is set to “0”. The processing routine is then terminatedfor the present.

On the other hand, when it is determined that the eccentricity profilePREcc has been generated (S21: YES), the process proceeds to the nextstep S23. In step S23, the tension F/F correction amount ΔDRff iscalculated. In other words, the tension F/F unit M13 acquires thecurrent rotation angle θr of the roll motor 22, and reads out a tensioncorresponding to the acquired rotation angle θr from the eccentricityprofile PREcc. Further, the tension F/F unit M13 calculates the tensionF/F correction amount ΔDRff such that the smaller read-out tensionresults in a greater tension F/F correction amount ΔDRff, for example.Then, the processing routine is terminated for the present.

Next, a processing routine to be performed by the first calculation unitM18 of the control device 50 to calculate the tension F/B correctionamount ΔDRfb will be described with reference to FIG. 8. This processingroutine is repeatedly performed in each tension detection cycle Ttdcwhen the medium 100 is transported by the transport device 20.

In a first step S31 of the processing routine, it is determined whetheror not the constant speed segment RC is selected from among the segmentsRA, RC, and RD in the speed profile PRV in calculation of the speed F/Bcorrection amount ΔDTfb. In other words, when the speed F/B unit M34performs the feedback control based on the target transport speed VTSTrin the constant speed segment RC in the speed profile PRV, the firstcalculation unit M18 determines that the constant speed segment RC isselected. On the other hand, when the speed F/B unit M34 performs thefeedback control based on the target transport speed VTSTr in theacceleration segment RA or the deceleration segment RD, the firstcalculation unit M18 does not determine that the constant speed segmentRC is selected.

When it is determined that the constant speed segment RC is selected(S31: YES), the process proceeds to a next step S32. In step S32, thegain of the feedback control for calculating the tension F/B correctionamount ΔDRfb is set to a smaller value as compared to when it is notdetermined that the constant speed segment RC is selected. Then, theprocess proceeds to a next step S33. In step S33, the set gain is usedto calculate the tension F/B correction amount ΔDRfb by feedback controlbased on the deviation between the target tension TENTr and the detectedtension value TENd. Then, the processing routine is terminated for thepresent.

On the other hand, when it is not determined that the constant speedsegment RC is selected (S31: NO), it can be determined that a segmentother than the constant speed segment RC is selected, and thus, theprocess proceeds to a next step S34. In step S34, the gain of thefeedback control for calculating the tension F/B correction amount ΔDRfbis set to a larger value as compared to when it is determined that theconstant speed segment RC is selected. Then, the process proceeds tostep S33. In step S33, the set gain is used to calculate the tension F/Bcorrection amount ΔDRfb by feedback control based on the deviationbetween the target tension TENTr and the detected tension value TENd.Then, the processing routine is terminated for the present.

Note that the gain in the embodiment includes a proportional gain usedin calculation of a proportional element, an integral gain used incalculation of an integral element, and a differential gain used incalculation of a differential element. As the proportional gainincreases, the absolute value of the proportional element increases. Asthe integral gain increases, the integral element increases. As thedifferential gain increases, the differential element increases. Whendifferent gains are used based on the type of the segment, i.e., theacceleration segment RA, the constant speed segment RC, or thedeceleration segment RD, any of the proportional gain, the integralgain, and the differential gain may be changed, or some of the gains maybe changed while the other gain(s) may not be changed.

Next, a medium transport method in the recording device 10 will bedescribed with reference to FIG. 9. In the embodiment, steps included inthe medium transport method are performed by the control device 50. Asillustrated in FIG. 9, in step ST101, a detected tension value TENdbeing a tension applied to the tension adjustment portion 100 a of themedium 100 is derived. Further, in step ST102, the tension F/Bcorrection amount ΔDRfb is calculated by feedback control based on thedeviation between the target tension TENTr and the detected tensionvalue TENd. Further, in step ST103, the tension F/F correction amountΔDRff is calculated by the feedforward control based on the eccentricityprofile PREcc. Further, in step ST104, the driving force DR by the rollmotor 22 is calculated based on the calculated tension F/B correctionamount ΔDRfb and the tension F/F correction amount ΔDRff. Further, instep ST105, the roll motor 22 is driven based on the calculated drivingforce DR.

The steps ST101 to ST105 are performed in each tension detection cycleTtdc shorter than the transport cycle Ttc.

The operations and effects of the embodiment will now be described.

(1) The tension F/B correction amount ΔDRfb is calculated by feedbackcontrol based on the target tension TENTr and the detected tension valueTENd in each tension detection cycle Ttdc is shorter than the transportcycle Ttc. Further, the driving force DR by the roll motor 22 iscalculated based on the tension F/B correction amount ΔDRfb, and theroll motor 22 is controlled based on that driving force DR. As a result,it is possible to reduce, in the transport cycle Ttc, divergence betweenthe target tension TENTr and a tension applied to the tension adjustmentportion 100 a of the medium 100.

(2) In the embodiment, as illustrated in FIG. 4, the target tensionTENTr varies within the transport cycle Ttc. Thus, when the detectedtension value TENd is detected in the n-th tension detection cycle Ttdcin the transport cycle Ttc, the target tension TENTr corresponding tothe n-th tension detection cycle Ttdc is read out. Further, the tensionF/B correction amount ΔDRfb is calculated by feedback control based onthe deviation between the read-out target tension TENTr and the detectedtension value TENd in the n-th tension detection cycle Ttdc. Then, thedriving force DR by the roll motor 22 is calculated based on the tensionF/B correction amount ΔDRfb.

Thus, even when the target tension TENTr varies within the transportcycle Ttc, it is possible to set the driving force DR by the roll motor22 to a value in which the variation of the target tension TENTr istaken into account. Further, based on the driving force DR obtained bythe calculation, the roll motor 22 is controlled. As a result, even whenthe target tension TENTr varies in the transport cycle Ttc, it ispossible to reduce divergence between the target tension TENTr and atension applied to the tension adjustment portion 100 a of the medium100.

(3) In the embodiment, the eccentricity state of the roll body R1 heldon the first rotary shaft 21 is acquired in the eccentricity measurementprocess, and the eccentricity profile PREcc is generated. After theeccentricity profile PREcc is generated, feedforward control based onthe eccentricity profile PREcc is performed to calculate the tension F/Fcorrection amount ΔDRff. Further, the driving force DR by the roll motor22 is calculated based on the tension F/F correction amount ΔDRff andthe tension F/B correction amount ΔDRfb, and the roll motor 22 iscontrolled based on the driving force DR. In this case, the correctiondelay of the driving force DR can be suppressed compared to whenfeedback control is performed without performing the feedforwardcontrol. As a result, the adjustment accuracy of the tension applied tothe tension adjustment portion 100 a of the medium 100 can be improved.

(4) In the eccentricity measurement process, fluctuation in the loadapplied to the roll motor 22 are monitored while the roll body R1 isrotated at a constant speed. Specifically, when an amount of the medium100 unwound from the roll body R1 per transport cycle Ttc by the firstdriving roller 23 and the first driven roller 24 is constant, the loadcurrent flowing through the transport motor 25 is measured at eachrotation angle θr. Further, based on the relationship between therotation angle θr and the load current obtained in the measurement, theeccentricity profile PREcc is generated. As a result, it is possible togenerate the eccentricity profile

PREcc based on the eccentricity state of the roll body R1.

(5) In the embodiment, the driving force DT by the transport motor 25 iscalculated based on the speed F/B correction amount ΔDTfb calculated bythe feedback control based on the target transport speed VTSTr and thedetected transport speed value VTSd of the medium 100. Further, thetransport motor 25 is controlled based on this driving force DT. Thus,even when the degree of tension applied to the tension adjustmentportion 100 a of the medium 100 fluctuates, it is possible to reducedivergence between the target transport speed VTSTr and the transportspeed of the medium 100 in a region downstream from the first drivingroller 23 and the first driven roller 24 in the transport direction X.By appropriately controlling the transport speed of the speed adjustmentportion 100 b of the medium 100 in this way, recording accuracy of theimage recorded onto the recording surface 101 of the medium 100 can beimproved.

(6) When the calculation result of the feedback control based on thetarget transport speed VTSTr in the acceleration segment RA of the speedprofile PRV is used to control the transport motor 25, the tensionapplied to the tension adjustment portion 100 a of the medium 100 tendsto increase, for example. Furthermore, when the calculation result ofthe feedback control based on the target transport speed VTSTr in thedeceleration segment RD of the speed profile PRV is used to control thetransport motor 25, the tension applied to the tension adjustmentportion 100 a tends to decrease, for example. In other words, when thecalculation result of the feedback control based on the target transportspeed VTSTr in a segment of the speed profile PRV other than theconstant speed segment RC is used to control the transport motor 25, thetension applied to the tension adjustment portion 100 a tends tofluctuate. On the other hand, when the calculation result of thefeedback control based on the target transport speed VTSTr in theconstant speed segment RC of the speed profile PRV is used to controlthe transport motor 25, the tension applied to the tension adjustmentportion 100 a tends to be constant.

Therefore, in the embodiment, it can be supposed that, when thecalculation result of the feedback control based on the target transportspeed VTSTr in a segment other than the constant speed segment RC isused to control the transport motor 25, the tension applied to thetension adjustment portion 100 a tends to fluctuate. Thus, the gain ofthe feedback control for calculating the tension F/B correction amountΔDRfb increases. As a result, even when there is a likelihood thattension applied to the tension adjustment portion 100 a fluctuates, itis possible to reduce divergence between the target tension TENTr and atension applied to the tension adjustment portion 100 a.

On the other hand, it can be supposed that, when the calculation resultof the feedback control based on the target transport speed VTSTr in theconstant speed segment RC is used to control the transport motor 25, thetension applied to the tension adjustment portion 100 a tends to beconstant. Thus, the gain of the feedback control for calculating thetension F/B correction amount ΔDRfb decreases. As a result, it ispossible to easily keep a state in which the detected tension value TENdconverges to the target tension TENTr. In other words, the tensionapplied to the tension adjustment portion 100 a can be controlled withhigh accuracy.

(7) In the embodiment, fluctuation in a tension applied to the tensionadjustment portion 100 a of the medium 100 is suppressed, and thus,fluctuation in the transport speed of the speed adjustment portion 100 bof the medium 100 can be suppressed. As a result, it is possible tosuppress deterioration in quality of an image recorded on the medium100.

Note that, the embodiments described above may be modified as follows.

-   -   In the above embodiment, the gain of the feedback control for        calculating the tension F/B correction amount ΔDRfb is changed        as appropriate, but the gain may not be changed.    -   The control for the transport motor 25 may not use the        calculation result of the feedback control based on the target        transport speed VTSTr.    -   The speed detection cycle Tsdc may not necessarily be shorter        than the tension detection cycle Ttdc, as long as the speed        detection cycle Tsdc is shorter than the transport cycle Ttc.        For example, the speed detection cycle Tsdc may have the same        length as the tension detection cycle Ttdc or may be longer than        the tension detection cycle Ttdc.    -   The eccentricity profile PREcc may not be a profile representing        a relationship between the rotation angle θr and the tension as        long as the eccentricity profile PREcc can represent an        eccentricity state of the roll body R1. For example, the        eccentricity profile PREcc may be a profile representing a        relationship between the rotation angle θr and the load applied        to the roll motor 22.    -   The eccentricity profile PREcc may be generated by using a        method different from the method described in the        above-described embodiment, as long as the eccentricity profile        PREcc can be generated. For example, the degree of eccentricity        with respect to the rotation angle θr may be measured by using        an optical sensor, instead of measuring the load current flowing        through the transport motor 25, to generate the eccentricity        profile PREcc based on the geometry of the roll body R1.    -   In the calculation of the driving force DR by the roll motor 22,        the feedforward control may not be performed, as long as the        feedback control is performed.    -   The recording device may be another type of printer different        from the serial scan type printer illustrated in FIG. 1, as long        as ink droplets can land on the speed adjustment portion 100 b        of the medium 100. For example, the recording device may be a        line printer in which a line printing method is adopted. A        record unit of the recording device using the line printing        method includes a line head having an elongated shape slightly        longer than the maximum width of the medium 100, in the width        direction intersecting the transport direction X.    -   The medium 100 may be a medium other than roll paper, as long as        the medium can be wound to form a roll. Examples of media other        than roll paper include films or sheets made of synthetic resin,        cloth, nonwoven fabrics, or laminate sheets.    -   The recording device 10 is not limited to a recording device        using drop discharging such as an ink-jet type device, and may        be a dot impact type device or an electrophotographic device.

Hereinafter, technical ideas that are understood from the aboveembodiments and modifications will be described in connection with theeffects.

A transport device includes a holding unit configured to rotatably holda roll body formed by winding a medium, a rotary driving unit configuredto impart, to the holding unit, a driving force in a rotation directionof the roll body, a transport unit disposed downstream from the holdingunit in a transport direction of the medium, the transport unit beingconfigured to feed, downstream in the transport direction and for eachpredetermined transport cycle, the medium unwound from the roll body, atransport driving unit configured to drive the transport unit, a controlunit configured to control the rotary driving unit and the transportdriving unit, a tension detection unit configured to derive, for eachtension detection cycle that is shorter than the transport cycle, adetected tension value that is a tension applied to a portion of themedium between the holding unit and the transport unit, and a tensionfeedback unit configured to calculate, each time the detected tensionvalue is detected, a tension feedback correction amount by feedbackcontrol based on a deviation between the detected tension value and atarget tension that is a target value of the detected tension value. Inthe transport device, the control unit is configured to calculate, foreach tension detection cycle, a driving force by the rotary driving unitbased on the tension feedback correction amount to control the rotarydriving unit based on the driving force by the rotary driving unit.

According to the above-described configuration, for each tensiondetection cycle shorter than the predetermined transport cycle, thetension feedback correction amount is calculated by feedback controlbased on the target tension and the detected tension value. Further, thedriving force by the rotary driving unit is calculated based on thetension feedback correction amount, and the rotary driving unit iscontrolled based on that driving force. As a result, it is possible toreduce, in the transport cycle, divergence between the target tensionand a tension applied to the portion of the medium between the holdingunit and the transport unit.

The above-described transport device may include a storage unitconfigured to store a transition of the target tension in the transportcycle, and when n is a natural number equal to or greater than 1 andcorresponds to an ordinal number of the tension detection cycle, thetension feedback unit may be configured to, when the tension detectionunit derives the detected tension value for n tension detection cycle inthe transport cycle, read out, from the storage unit, the target tensioncorresponding to the n tension detection cycle, and calculate thetension feedback correction amount by feedback control based on adeviation between the detected tension value for the n tension detectioncycle and the target tension that is read out from the storage unit.

According to the above-described configuration, even when the targettension varies within the transport cycle, it is possible to set thedriving force by the rotary driving unit to a value in which thevariation of the target tension is taken into account. Further, based onthe driving force obtained by the calculation, the rotary driving unitis controlled. As a result, even when the target tension varies in thetransport cycle, it is possible to reduce divergence between the targettension and a tension applied to the portion of the medium between theholding unit and the transport unit.

Note that “n” is a natural number equal to or greater than “1”. In otherwords, in each tension detection cycle in a single transport cycle, “n”is incremented by “1”. Further, when the transport cycle ends, “n” isreset to “0”.

The above-described transport device may include an eccentricity profilegenerating unit configured to perform an eccentricity measurementprocess for measuring eccentricity of the roll body held by the holdingunit, and the eccentricity profile generating unit configured togenerate an eccentricity profile based on an eccentricity state of theroll body measured in the eccentricity measurement process, and atension feedforward unit configured to calculate, for each tensiondetection cycle, a tension feedforward correction amount by feedforwardcontrol based on the eccentricity profile generated by the eccentricityprofile generating unit, and the control unit may be configured tocalculate, for each tension detection cycle, a driving force by therotary driving unit based on the tension feedback correction amount andthe tension feedforward correction amount to control the rotary drivingunit based on the driving force by the rotary driving unit.

The roll body held by the holding unit may be eccentric. Even when anamount of the medium unwound from the roll body per transport cycle,i.e. the amount of medium transported per transport cycle, is constant,such an eccentric roll body may lead to a fluctuation in tension due toa fluctuation in the load applied to the rotary driving unit, forexample.

According to the above-described configuration, the eccentricitymeasurement process is performed to generate an eccentricity profilebased on an eccentricity state of the roll body. Further, when theeccentricity profile is generated, feedforward control based on theeccentricity profile is performed to calculate the tension feedforwardcorrection amount. The driving force by the rotary driving unit iscalculated based on the tension feedforward correction amount and thetension feedback correction amount, and the rotary driving unit iscontrolled based on the driving force. In this case, the correctiondelay of the driving force by the rotary driving unit can be suppressedcompared to when feedback control is performed without performing thefeedforward control.

In the above-described transport device, in the eccentricity measurementprocess, the eccentricity profile generating unit may be configured togenerate the eccentricity profile based on a transition of load currentflowing in the transport driving unit with respect to a change in arotation angle of the roll body, in a state where the rotary drivingunit outputs a constant driving force substantially and a transportamount of the medium for each transport cycle is constant substantially.

Even when an amount of the medium unwound from the roll body pertransport cycle, i.e. the amount of the medium transported per transportcycle, is constant, an eccentric roll body may lead to a fluctuation intension due to a fluctuation in the load applied to the rotary drivingunit, for example. According to the above-described configuration, aneccentricity profile can be generated based on a transition in the loadcurrent flowing through the transport driving unit when the roll body isrotated at a constant speed. Accordingly, it is possible to indirectlymeasure fluctuations in the load applied to the rotary driving unitbased on the load current flowing through the transport driving unitwithout using a tension sensor or the like for measuring tensionfluctuations. As a result, it is possible to generate, by using a simpleconfiguration, the eccentricity profile based on the eccentricity stateof the roll body.

The above-described transport device may include a transport speedderiving unit configured to derive, in a speed detection cycle that isshorter than the transport cycle, the detected transport speed valuebeing a transport speed of the medium fed downstream in the transportdirection by the transport unit, and a speed feedback unit configured tocalculate a speed feedback correction amount by feedback control basedon a deviation between a target transport speed being a target value ofthe transport speed of the medium, and the detected transport speedvalue derived by the transport speed deriving unit, and the control unitmay be configured to calculate, for each speed detection cycle, adriving force by the transport driving unit based on the speed feedbackcorrection amount to control the transport driving unit based on thedriving force by the transport driving unit.

According to the above-described configuration, the driving force by thetransport driving unit is calculated based on the speed feedbackcorrection amount calculated by the feedback control based on the targettransport speed and the detected transport speed value of the medium,and the transport driving unit is controlled based on the driving force.Thus, even when the degree of tension applied to the portion of themedium between the holding unit and the transport unit fluctuates, it ispossible to reduce divergence between the target transport speed and thetransport speed of the medium in a region downstream from the transportunit in the transport direction.

The above-described transport device may include a speed profile storageunit configured to store a speed profile being a transition in thetarget transport speed over time in the transport cycle, the speedfeedback unit may be configured to read out, from the speed profilestored in the speed profile storage unit, the target transport speedcorresponding to a time in the transport cycle, the speed profile mayinclude an acceleration segment in which the transport speed of themedium increases over time substantially, a constant speed segmentfollowing the acceleration segment, the transport speed of the mediumbeing constant over time substantially, and a deceleration segmentfollowing the constant speed segment, the transport speed of the mediumdecreasing over time substantially, and the tension feedback unit may beconfigured to, when the speed feedback unit performs feedback controlbased on the target transport speed in the constant speed segment of thespeed profile, reduce a gain of feedback control for calculating thetension feedback correction amount, as compared to when the speedfeedback unit performs feedback control based on the target transportspeed in a segment other than the constant speed segment of the speedprofile.

When the calculation result of the feedback control based on the targettransport speed in the acceleration segment of the speed profile is usedto control the drive constant speed segment, the transport speed of themedium decreasing over time in the deceleration segment, the tensionapplied to the portion of the medium between the holding unit and thetransport unit tends to increase, for example. Furthermore, when thecalculation result of the feedback control based on the target transportspeed in the deceleration segment of the speed profile is used tocontrol the drive constant speed segment, the transport speed of themedium decreasing over time in the deceleration segment, the tensionapplied to the portion of the medium between the holding unit and thetransport unit tends to decrease, for example. In other words, when thecalculation result of the feedback control based on the target transportspeed in a segment of the speed profile other than the constant speedsegment is used to control the drive constant speed segment, thetransport speed of the medium decreasing over time in the decelerationsegment, the tension applied to the portion of the medium between theholding unit and the transport unit tends to fluctuate. On the otherhand, when the calculation result of the feedback control based on thetarget transport speed in the constant speed segment of the speedprofile is used to control the drive constant speed segment, thetransport speed of the medium decreasing over time in the decelerationsegment, the tension applied to the portion of the medium between theholding unit and the transport unit tends to be constant.

Therefore, according to the above-described configuration, when it canbe supposed, based on the control manner of the transport unit, that thetension applied to the portion of the medium between the holding unitand the transport unit is likely to fluctuate, the divergence betweenthe tension applied to that portion and the target tension is likely toincrease. Thus, the gain of the feedback control for calculating thetension feedback correction amount increases. As a result, even whenthere is a likelihood that a tension applied to the portion of themedium between the holding unit and the transport unit fluctuates, it ispossible to reduce divergence between the target tension and a tensionapplied to that portion.

On the other hand, when it can be supposed, based on the control mannerof the transport unit, that the tension applied to the portion of themedium between the holding unit and the transport unit is not likely tofluctuate, the divergence between the tension applied to that portionand the target tension is not likely to increase. Thus, the gain of thefeedback control for calculating the tension feedback correction amountdecreases. As a result, the control performance can be improved.

A recording device may include the above-described transport device, anda recording unit configured to perform recordning onto a portion of themedium to be transported by the transport device, the portion beinglocated downstream from the transport unit in the transport direction.

According to the above-described configuration, a fluctuation in atension applied to the portion of the medium between the holding unitand the transport unit is suppressed, and thus, a fluctuation in thetransport speed of the portion of the medium onto which the recording isperformed by the recording unit can be suppressed. As a result, it ispossible to suppress deterioration in quality of an image recorded onthe medium.

A medium transport method includes providing, a transport deviceincluding a holding unit configured to rotatably hold a roll body formedby winding a medium, a rotary driving unit configured to impart, to theholding unit, a driving force in a rotation direction of the roll body,a transport unit disposed downstream from the holding unit in atransport direction of the medium, the transport unit being configuredto feed the medium, unwound from the roll body, downstream in thetransport direction for each predetermined transport cycle, and atransport driving unit cinfigured to drive the transport unit. Themedium transport method further includes deriving, for each tensiondetection cycle that is shorter than the transport cycle, a detectedtension value that is a tension applied to a portion of the mediumbetween the roll body and the transport unit, calculating, each time thedetected tension value is derived, a tension feedback correction amountby feedback control based on a deviation between the detected tensionvalue and a target tension that is a target value of the detectedtension value, and calculating, for each tension detection cycle, adriving force by the rotary driving unit based on the calculated tensionfeedback correction amount to drive the rotary driving unit based on thedriving force by the rotary driving unit.

The control device of the transport device is caused to perform theabove-described medium transport method to achieve the same effects asthose of the transport device described above.

What is claimed is:
 1. A transport device comprising: a holding unitconfigured to rotatably hold a roll body formed by winding a medium; arotary driving unit configured to impart, to the holding unit, a drivingforce in a rotation direction of the roll body; a transport unitdisposed downstream from the holding unit in a transport direction ofthe medium, the transport unit being configured to feed, downstream inthe transport direction and for each predetermined transport cycle, themedium unwound from the roll body; a transport driving unit configuredto drive the transport unit; a control unit configured to control therotary driving unit and the transport driving unit; a tension detectionunit configured to derive, for each tension detection cycle that isshorter than the transport cycle, a detected tension value that is atension applied to a portion of the medium between the holding unit andthe transport unit; and a tension feedback unit configured to calculate,each time the detected tension value is detected, a tension feedbackcorrection amount by feedback control based on a deviation between thedetected tension value and a target tension that is a target value ofthe detected tension value, wherein the control unit is configured tocalculate, for each tension detection cycle, the driving force by therotary driving unit based on the tension feedback correction amount tocontrol the rotary driving unit based on the driving force by the rotarydriving unit.
 2. The transport device according to claim 1, comprising astorage unit configured to store a transition of the target tension inthe transport cycle, wherein when n is a natural number equal to orgreater than 1 and corresponds to an ordinal number of the tensiondetection cycle, the tension feedback unit is configured to, when thetension detection unit derives the detected tension value for an ntension detection cycle in the transport cycle, read out, from thestorage unit, the target tension corresponding to the n tensiondetection cycle, and calculate the tension feedback correction amount byfeedback control based on a deviation between the detected tension valuefor the n tension detection cycle and the target tension that is readout from the storage unit.
 3. The transport device according to claim 1,comprising: an eccentricity profile generating unit configured toperform an eccentricity measurement process for measuring eccentricityof the roll body held by the holding unit, and the eccentricity profilegenerating unit configured to generate an eccentricity profile based onan eccentricity state of the roll body measured in the eccentricitymeasurement process; and a tension feedforward unit configured tocalculate, for each tension detection cycle, a tension feedforwardcorrection amount by feedforward control based on the eccentricityprofile generated by the eccentricity profile generating unit, whereinthe control unit is configured to calculate, for each tension detectioncycle, the driving force by the rotary driving unit based on the tensionfeedback correction amount and the tension feedforward correction amountto control the rotary driving unit based on the driving force by therotary driving unit.
 4. The transport device according to claim 3,wherein in the eccentricity measurement process, the eccentricityprofile generating unit is configured to generate the eccentricityprofile based on a transition of a load current flowing in the transportdriving unit with respect to a change in a rotation angle of the rollbody, in a state where the rotary driving unit outputs a constantdriving force substantially and a transport amount of the medium foreach transport cycle is constant substantially.
 5. The transport deviceaccording to claim 1, comprising: a transport speed deriving unitconfigured to derive, for each speed detection cycle that is shorterthan the transport cycle, a detected transport speed value, the detectedtransport speed value being a transport speed of the medium feddownstream in the transport direction by the transport unit; and a speedfeedback unit configured to calculate a speed feedback correction amountby feedback control based on a deviation between a target transportspeed that is a target value of the transport speed of the medium andthe detected transport speed value derived by the transport speedderiving unit, wherein the control unit is configured to calculate, foreach speed detection cycle, a driving force by the transport drivingunit based on the speed feedback correction amount to control thetransport driving unit based on the driving force by the transportdriving unit.
 6. The transport device according to claim 5, comprising aspeed profile storage unit configured to store a speed profile that is atransition of the target transport speed over time in the transportcycle, wherein the speed feedback unit is configured to read out, fromthe speed profile stored in the speed profile storage unit, the targettransport speed corresponding to a time in the transport cycle, thespeed profile includes an acceleration segment in which the transportspeed of the medium increases over time substantially, a constant speedsegment that follows the acceleration segment and in which the transportspeed of the medium is constant over time substantially, and adeceleration segment that follows the constant speed segment and inwhich the transport speed of the medium decreases over timesubstantially, and the tension feedback unit is configured to, when thespeed feedback unit performs feedback control based on the targettransport speed in the constant speed segment of the speed profile,reduce, as compared to when the speed feedback unit performs feedbackcontrol based on the target transport speed in a segment other than theconstant speed segment of the speed profile, a gain of feedback controlfor calculating the tension feedback correction amount.
 7. A recordingdevice, comprising: the transport device according to claim 1; and arecording unit configured to perform recording onto a portion of themedium transported by the transport device, the portion being locateddownstream from the transport unit in the transport direction.
 8. Amedium transport method comprising: providing, a transport deviceincluding a holding unit configured to rotatably hold a roll body formedby winding a medium, a rotary driving unit configured to impart, to theholding unit, a driving force in a rotation direction of the roll body,a transport unit disposed downstream from the holding unit in atransport direction of the medium, the transport unit being configuredto feed the medium, unwound from the roll body, downstream in thetransport direction for each predetermined transport cycle, and atransport driving unit configured to drive the transport unit; deriving,for each tension detection cycle that is shorter than the transportcycle, a detected tension value that is a tension applied to a portionof the medium between the roll body and the transport unit; calculating,each time the detected tension value is derived, a tension feedbackcorrection amount by feedback control based on a deviation between thedetected tension value and a target tension that is a target value ofthe detected tension value; and calculating a driving force by therotary driving unit based on the tension feedback correction amountcalculated, to drive the rotary driving unit based on the driving forceby the rotary driving unit.